Reliability and validity of a backlighted digitizer when used for craniofacial measurements

In this study the precision and validity of digitized measurements were tested for a specific, commercially available, backlighted digitizer. The tests were based on the repeated and systematic recordings of equally spaced points on a printed millimeter grid and on the repeated recordings of selected points on radiographic duplicating film and tracing acetate, with and without backlighting. Cursor and carrier position relative to the tablet, and tablet position relative to the monitor, proved to be important. The backlighting produced systematic bias due to the heating effect on both the duplicating film and the tracing acetate.